Magnetic Field from Current Carrying Wire

Electrons are going around a circle in a counterclockwise direction as shown. At the center of the circle they produce a magnetic field that is:

• into the page
• out of the page
• to the left
• to the right 

In the figure, the current element , the point P, and the three vectors (1, 2, 3) are all in the plane of the page. The direction of , due to this current element, at the point P is:

• into the page
• out of the page 
• in the direction marked "3" 
• in the direction marked "1"

Two long straight wires are parallel and carry current in the same direction. The currents are 8.0 and 12 A and the wires are separated by 0.40 cm. The magnetic field at a point midway between the wires is: 

• 0 T
• 4.0 ´ 10^–4 T
• 8.0 ´ 10^–4 T
• 12 ´ 10^–4 T

A long straight wire carrying a 3.0 A current enters a room through a window 1.5 m high and 1.0 m wide. The path integral ∮B*ds around the window frame has the value: 

• 0.20 T×m
• 2.5 ´ 10^–7 T×m
• 3.0 ´ 10^–7 T×m
• 3.8 ´ 10^–6 T×m

In the figure, there are three wires carrying currents in the indicated directions, and an Amperian loop. The sign of the contribution of the current in each wire to the path integral  in Ampere’s Law is:

• i₁ +, i₂ –, i₃ 0
• i₁ –, i₂ +, i₃ 0
• i₁ +, i₂ +, i₃ –
• i₁ –, i₂ –, i₃ +

Two long straight wires enter a room through a window. One carries a current of 3.0 A into the room while the other carries a current of 5.0 A out. The magnitude of the path integral ∮B*ds around the window frame is: 

• 2.5 ´ 10^–6 T×m
• 3.8 ´ 10^–6 T×m
• 6.3 ´ 10^–6 T×m
• 1.0 ´ 10^–5 T×m

A long straight cylindrical shell carries current i uniformly distributed over its cross section. The magnitude of the magnetic field is greatest: 

• at the inner surface of the shell
• at the outer surface of the shell 
• inside the shell near the middle 
• in hollow region near the inner surface 

Magnetic field lines inside the solenoid shown are:

• clockwise circles as one looks down the axis from the top of the page 
• counterclockwise circles as one looks down the axis from the top of the page 
• toward the top of the page 

A solenoid is 3.0 cm long and has a radius of 0.50 cm. It is wrapped with 500 turns of wire carrying a current of 2.0 A. The magnetic field at the center of the solenoid is: 

• 9.9 ´ 10^–8 T
• 1.3 ´ 10^–3 T
• 4.2 ´ 10^–2 T
• 16 T

The diagram shows three arrangements of circular loops, centered on vertical axes and carrying identical currents in the directions indicated.  Rank the arrangements according to the magnitudes of the magnetic fields at the midpoints between the loops on the central axes, from least to greatest.

• 1, 2, 3
• 2, 1, 3
• 2, 3, 1
• 3, 2, 1